The Influence of Zirconia Powder Dispersion Technique on Microstructure and Properties of Al2O3 – ZrO2 Ceramic

The results of microstructure and mechanical properties investigation for alumina and zirconia toughened alumina (ZTA) with 20 wt. % 3Y-ZrO2is presented. It was stated that the technique of preliminary treatment for zirconia suspension makes significant influence on sintered specimen microstructure. Introduction of the alloying additive treated with ball milling reduces Al2O3grain size in ceramic from 2-5 μm to 0.2-1 μm. The reduction of grain size increases the bending strength of ceramic material from 270 MPa up to 350 MPa. However fracture toughness of alumina and ZTA is 3.4 and 2.5 MPa·m1/2, respectively. It was shown that the low level of mechanical properties is related to the occurrence of major defects in the form of granule boundaries preserved at the forming stage.

Comparison between Slip Casting and Cold Isostatic Pressing for the Fabrication of Nanostructured Zirconia

Consolidation of ceramic parts may be achieved by several techniques, including the slip casting and cold isostatic pressing (CIP) methods. In the present work, the performances of the two methods are compared in the fabrication of nanostructured zirconia compacts for dental crown applications. First, a zirconia suspension suitable for slip casting was prepared. The rheological properties of the zirconia suspension were optimized by adding a dispersant agent and controlling the pH. Zirconia slurries were then slip-cast into a pellet. Second, another group of zirconia pellets were fabricated using uniaxial pressing and were then cold-isostatically pressed. Both slip-cast and CIP samples were sintered at 1300 °C with a soaking time of 2 hrs. The mechanical properties of both samples were compared. The samples prepared by slip casting were denser compared with those prepared via CIP. Slip casting technique produced samples with 98.8% of the theoretical density, which resulted in the high Vickers hardness (11.4 GPa) of the slip-cast samples. Morphological studies revealed that the microstructures of the slip cast-sample were more homogeneous and contain no porosity. The formation of such a structure is due to the enhancement of the particle packing efficiency by slip casting as well as to the removal of larger agglomerates by colloidal processing prior to casting. As a consolidation stage, slip casting appears to be more suitable than the CIP technique in preparing reliable nanostructural ceramic parts.

Preparation of Ultrafine Zirconia Suspension Using Glutin-Urea Gelcasting System

Glutin-urea system was used to prepare ultrafine zirconia suspension for gelcasting. Premixed solution was prepared at deionized water/glutin/urea ratio of 90/10/5 (by weight). Adjusting pH value to11, zirconia powders and A-type dispersant (polyacrylic salt) were added. After ball-milled about 12 hours, 45vol% zirconia slurry was acquired and the viscosity of which was less than 1 PaS.

Effect of Dispersant Agent Amount in Colloidal Processing of Zirconia Dental Ceramic

The effects of a polyelectrolyte dispersant agent, polyethyleneimine (PEI), on the rheology of zirconia 3Y-TZP suspensions and the densification characteristics of sintered zirconia were investigated. The colloidal processing technique was used to minimize the agglomeration of nanoparticles during the fabrication of the samples. Five batches of 10% zirconia suspensions containing different amounts of PEI at 0.3, 0.4, 0.5, 0.6, and 0.7 wt% were prepared. The rheological properties of the zirconia suspensions were determined using a rotational viscometer. The optimum amount of PEI that can maximize powders dispersion was determined. The green samples were then prepared using the slip casting process. The samples were densely sintered at a final sintering temperature of 1300 °C. The result revealed that the zirconia suspension with 0.5 wt% PEI was the most optimum amount to obtain a well-dispersed suspension. The sintered density of zirconia 3Y-TZP reached its maximum by adding 0.5 wt% PEI.